CA2206521C - Video modem - Google Patents

Abstract

An apparatus and method is provided for modulating and transmitting full-motion, television quality color video signals along with digital data signals over a pair of ordinary unshielded twisted pair telephone wires (UTP) without interfering with normal telephone data on the wires. The invention is characterized by a transmission method involving frequency modulation (VCO1) of a baseband video signal and subsequent filtering (BPF1) to suppress an upper sideband corresponding to a color component of the original signal. The filtered signal is received from the telephone wires at a different location, filtered, demodulated and provided to a display device. Full-duplex modulation over the same pair of wires is possible, such that two video signals may be simultaneously transmitted, each signal having an approximate bandwidth of 6 MHz and shifted to a desirable non-interfering frequency location within the approximately 20 MHz of useable bandwidth on the telephone wires. No pre-emphasis or de-emphasis is required to achieve good quality video transmission.

Description

VIDEO MODEM
BACKGRQUND OF THE INVENTION
1. Technic~l Field This invention relates generally to tr~n~mi~ion of full-motion, television-quality color video signals and associated data and audio signals over ordinary n~hiekle~l twisted pair (UTP) t~oleph--n~- wiring and, more particularly, to an a~ardlus and method for bidirectionally l.,...~;...;ll;..~ such signals over a telephone wire without il.L~.re~ g with normal telephone signals on the wire.

2. Related Information Un~hi~l-ie~l twisted pair (UTP) wiring is used in many office buildings to transmit voice grade signals and low-speed data such as that gellelaL~d by modems. Such wiring normally runs be~weell 20 and 2,000 feet from a central switch or entry point to a particular telephone. A private branch e,~ e (PBX) is often used to comlecl the building wiring lleLWoll~ to an external set of telephone lines provided by a telephone CO~ )ally.
Beyond an office bl1ilAin~, however, tclel)holl~ co. . ~ . ~ies typically restrict the bandwidth of a particular outside "line" to no more than about 4 KHz, severely halll~elillg the ability to transmit allyLllillg other than very low bandwidth data over long ~ s As is self-evident, a typical NTSC television signal reqniring ~lv~hllat~ly 6 MHz of bandwidth cannot be directly tr~n~nitte-l over such lines. Some compani~o~ have attempted to compress and otherwise ~ ulate various types of video signals to fit within the limited WO 96~17474 P~ sll4946 bandwidth of telephone wires. A ~~r~s~.llali-le example of such a system is disclosed in U.S. Patent No 5,164,980 to Bush et al. (video telephone system).
Within an office building, however, the telephone wiring is not arti~lcially limited in bandwidth, but instead suffers from the ihherent t~ ioll qualities of the wiring such as phase shifts and ~ on at higher frequencies. Thus, s~ ric~ y higher data tr~n~mi~ion bandwidths may be achieved within an office building or other ~lluc;lul~ having similar wiring arrangçm~ntc. lHowever, the wiring trancmicsion effects can cause drastic changes in received waveforms.These effects, while quite tolerable in voice co,~ Al ions, destroy the integrity of individual pulses of a baceb~ video signal. For example, all~lllpling to di.~lly L~ lllil a b~ceb~ NTSC video signal over UTP wiring in a bl~iklin~ would result in a wholly unacceptable result (and would also ,llL~L~ with normal telephone data). Amplitude mo ~ ting such a signal (as is done in TV tr~ncmittPrs) also would result in an unacceptable result. As shown in the following Table 1, the typical ~llr~ ion loss as a function of fi~luell~;y along 2,000 feet of UTP wire is severe:

FREQ (MHz) LOSS (dB) Various sc-h~m~s have been developed in an attempt to o~,lcoll.e the above problems and others. For example, some sch~me~C involve se~a,dtil.g various components of an NTSC signal (such as a lllmin~nre signal and a chr~min~nr~
signal) and sel)al~lely mod~ fin~ and tr~n~mittin~ them. One example of such S a scheme is illustrated in U.S. Patent 4,955,048 to Iw~lulil et al. However, such scllPm~s often require complex and eA~.ensive signal proceesin~ circuits and may be particularly sensitive to device tole,dllces.
Video teleconfc.~ ,illp systems are known in which two-way visual and audio co.. ~ ;c~tiQn is possible be~ individuals or groups at different locations. Video col~r~,lleillg systems, however, require expensive equipment, high bandwidth co....-~ tion ch~nn~lc, and fiber optic or other high bandwidth wiring throughout a building. High qualit,v video col~lc~ lg over exi.cting lelt,~holle wiring has h~l.,lofol~ been ~iffi--l-lt eA~l~ive, or impossible in many cases. For these r~asol~s, a need exists for providing an inexpensive telecol~r~nc,llg method and a~palalus for use within bl-iklin~.c which have ordilla,~ tclephoue wiring, without ~ Lhillg special wiring or ~A~enshre tr~ncmicsi-)n eqnirm~rlt SUMMARY OF THE INVENTION
The present invention solves the aforementioned problems by providing a method and appalaLus for hl~A~IL~ively tr~ full-motion, television-quality color video signals and other signals over ordinary nnchi~lde~ t~visted pair (UTP) telephone wires. The invention is characterized by a tr~ncmi~cion method wo 96rl7474 PCrlUS9S/14946 which allows two NTSC composite signals, along with data and audio signals, to be sim~ Pou~ly ll~ d bidirectionally over a single pair of wires willluul hl~e~ g with normal voice data and other signals tr~n~mitted on the same pair of wires.
S In various l)rer~ d embor1im~ntc, an NTSC signal is tr~n~mit~P-l using an FM signal having a low modulation index and a :~ul~plcssed upper sideb~n-l In a typical telephone in~t~ tion, the cable run length belweell the central switch or entry point to the telephone itself can vary, but is usually b~l~ecll 20 and 2,000 feet. By using frequency modulation, the demodulator can amplify and then limit the received signal. No adjl~tm~t~ are required to-set up the demodulator for each cable run.
Other fcalu,cs and advantages of the invention will become a~pa~ L
through the following ~et~il~ descli~lion and dl~wings.
BRIEF DESCRIPIION OF THE DRAVVINGS
FIG. 1 shows a frequency ~ecllulll for a composite NTSC television signal. FIG. 1(a) shows the spectrum distribution for an NTSC color signal at basebal~d; FIG. 1(b) shows a full amplitude mo~lul~t~-l NTSC signal; and FIG.
l(c) shows a vestigial ~icleb~nfl AM modulated signal, the lower picture sideband having been ~ubst~nti~lly ~emoved.
FIG. 2 shows a frequency plan for use in allocating signals to frequency bands in a single telephone-grade wire in accol ial,ce with the present invention.

WO 96/17474 PCI'/US95/14g46 FIG. 3 is a simplified block diagram showing components used to sim~ P~usly t~ncmit and receive two NTSC signals in accordance with the principles of the present invention.
FIG. 4 is a more det~iltod circuit SC~ .AI;C illusll~tin~ specific S co.ll~ollelll~ which may be used in a trAn~mit/receive circuit.
FIG. S shows how data displayed on co---~ monitor may be tr~ncmi1tecl over telephone lines in accolddnce with the invention.
DETAILED DESCRIPrION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows the ..~e~l.ul,l of a typical NTSC television signal. As shown in FIG. 1(a), a bAc~A~l colllposilc NTSC video signal occupies approximately 4.2 MHz of bandwidth, inrl~ ing l-~...i..A~-~e signal L, color S11bCA~ CSC~ and color signals C CO---~ g chl.~ A~.~e illro...~tion (hue and s~At~ ti~n) A sound carrier SC also may be provided with the video signal to llal~.lllil audio il,ro~l"alion. ~lth~llgh not explicitly shown in FIG. 1(a), the well-known NTSC signal collll,lis~r. various other s.yll~l~O~ illg signals needed to reconstruct the original signal at the 1~;-~l. Details of the signal ~lluclulc are set forth in ~ldllddlls prnmlllg~tYI by the FCC (FCC Rules, 47 C.F.R.
73.699, h,col~ aled herein by I cÇclcllce).
When the baseband NTSC signal is used to amplitude modulate a carrier signal, the bandwidth is typically doubled, to at least 8.4 MHz. As shown in FIG. l(b), the process of amplitude modulation using the baceb-An-l video signal produces a signal having an upper picture sideband UPSB and a lower picture WO 96/17474 ~ 3114946 sideband LPSB centered around the picture carrier PC. Both sidebands in any signal contain all the n~çscAry intelligence to recreate the original information.
An audio ~ul~ca~l;el ASC inf ~ leC two audio sidebands ASB.
As shown in FIG. l(c), commercial television tr~n~mitting stations use vestigial .ci~lebAntl AM Ll,.~ iceion~ The tr~n.~mitfing eqllirln~ont ~.u~ s~.es the lower picture sideband in order to reduce the required bandwidth (hence the term, "vestigial si~leb~n~l modulation"). The lower si~leb~nrl is mostly removed, leaving only a "vestige" in ~rlr1itinn to the upper sitlebAn-l. This allows commPrcial TV to be trAncmitte~l with a 6 MHz channel spacing, in-~hl(lin~ audiocarriers and guard bands, so that many TV stations can .cimllltAntoously broadcast without i..l~lr~ ,g with each other.
Bandwidth is much more limited on UTP telephone wires. To achieve a 2,000 foot tr~ncmiccion ~ tAn~e~ it is necec~A, y to limit the total tr~cmi~sionbandwidth to less than 20 MHz. As pointed out previously, alLt;lll~lillg to transmit an amplitude modulated video signal (such as is done with comm~rcial television ~ S) is not feasible over ol~ / telephone wire due to severe llA~ ion effects including distortions which cause unacceptable group delays.
Although the use of frequency or phase modlllAtion instead of amplitude modulation could mitig~te some of these effects, the bandwidth required would be prohibitive.
Even with narrow deviation FM, a frequency mo~ AtY1 carrier produces a signal spectrum that is a least twice the baseband frequency. For video signals, WO 96117474 PCr/US95/14946 that would require a minimnm of 10 MHz per rh~nnPI For full-duplex operation (i.e., siml-lt~nPously tl~l~cll~ ;llg video signals in both directions over the same wire), two 10 MHz çh~nnPI~ would be nPetle~l, which would consume all of the practically available bandwidth with no guarlib~n~s.
To overcome the afolcnl~nlionp-d limit~tions, the present invention contemplates the use of a "vestigial sideband FM" signal. This means that one of the FM modulation sidebands is removed at the tr~n~mittPr, preferably the upper si~l~pb~n-l for reasons that will become a~ar~.lL. By using this type of modulation, the original NTSC b~CPb~n~l signal can be reconstructed using only 6 MHz of bandwidth while allowing for a few mPg~hPrtz of hl~.ch ~mel guard band. The 6 MHz band can include a broadcast quality video signal and the ~r~-,...p~..yi,~g audio signal, ~lth()l-~h in various emboAimPnt~ the audio signal is filtered out along with the upper ~ Pb~n~ One or more CD-quality audio signals may also be n~ using a se~ e data rh~nnPI
It should be recognized that the principles of the present invention may also be used with PAL and SECAM-type television ~ign~l~, with a~lul~lid~
mo~ifi-~tions in the bandwidths and center frequPnriPs to ~ccommndate the dirr~lcllces in spectra. For e,.~.lple, instead of 6 MHz cl~nnPI bandwidth, PAL
~ and SECAM systems can employ 7-8 MHz channel bandwidths. Details of the 2Q PAL and SECAM signal structure are well known, and are not repeated here.Although AM and nallo~l,~ d FM have similar frequency spectra, they are ~ tin~tively different methods of modulation. In the AM case, the carrier envelope is varied, the frequency reTn~inin~ lnrh~nged; in the FM case, the carrier amplitude is ~llm~d to be co~ct~nt the phase (and in~t~nt,.n~ouc frequency) varying with the signal. It should be noted that using a low PM
modulation index would appear to defeat many of the advantages gained by using S FM m~l~ tion in the first place but, as described herein, the r~snlting signal is suitable for tr~n~mittin~ television-quality ~icLu,eF. over ordinary telephone wire, even without using tr~lition~l Pmrh~ mrh~ic r~h~ uill~. The use of a smaller modulation index helps pr~ e.lL phase shifts which would occur at higherdeviations.
As shown in FIG. 2, the present invention colllclll~lates a frequency plan which allows for several signals to be simnlt~n~ously tr~n~mitte~l within the bandwidth available on UTP wire. In FIG. 2, ~mplitllde is i~le~.ell~ed on the vertical axis and frequency in m~g~h~rtz is 1~l, sellL~d on the hGli~ollL~l axis.
A number of signals are allocated in the frequency band endinB at about 20 MHz, the plGrell~d limit for lln~hiP~ d telephone wire as contemplated in the present invention. As described in more detail below, video signals A and B
may be used for tr~n~mitting video-quality images across the UTP wire.
A first signal T lGplC,3el1lS ~Yi~ , telephone signals at the very low end of the ~.~ecL.ul.l. These signals may be analog or digital. In either case, their spectrum components are normally much less than 1 MHz.
Data signals Dl and D2 may be centered about 1.5 MHz and 3.5 MHz, respectively, and may be used to transmit high-speed data bidirectionally across wo 96/17474 PCTIIJS9S/14946 the wire using any of various well known modulation mlotho lc (inrllJ-~in~ PSK, QAM, or FSK modulations). Al~ ly, data signals Dl and D~ may each co",~lise an FM signal (FMl and FM2, respectively), for 1l~ r~ uel~y mo~lnl~t~l audio data corresponding to video si'gnals A and B, r~ e~ cly.
Moreover, digital data signals Digl and Dig2 l~presenl digitally mol~ tod data ~l1~IS which may also acco,ni)an~ video signals A and B. Thus, each data signal Dl and D2 may comprise any of various types of signal modulation which may be used to transmit i~lr(~.,..~tion which is preferably related to co".,,,~onding video signals A and B r~i,pe~;lively. The exact frequency pl~em~rlt of data signals Dl and D2 may be varied, c ~ with telephone signal T and video signals A and B.
A carrier for video tr~n.cmimor signal A is illustrated as being ce~ .,d about 9 MHz and a carrier for video tr~ncmhter signal B is illllctrated as being cellt~lcd about 17 MHz. An "outer" lower cideb~n-l of signal A (corresponding to the color subcarrier) is l~plese~led by LSB", while an "outer" lower sideband of signal B (co~ onding to the color ~ubca~-icr) is l~lesenled by LSBB- The upper sidebands cont~ining the color subcalliel signals have been ~u~.~ssed in FIG. 2 and are thus not shown. The sound carriers, located above the upper color sidebands, have also-been ~u~ sed and are not shown.
In accordance with the frequency plan of FIG. 2, two video signals may be simnl~ ously tr~n~mitt~ across a single wire, each having an approxim~t~
bandwidth of 6 MHz. It should be noted that the illustrated center frequencies CA 02206~21 1997-0~-30 wo 96/17474 Pcrluss5ll4946 of the video and data signals are by way of example only, and it is of course possible to move these signals around within the approximately 20 MHz of usable bandwidth or even beyond (if one is willing to accept lower quality picture signals). Moreover, it may be possible to use bandwidths of less than 6 MHz for each video signal, with readily recognizable tradeoffs in picture quality and the like.
Good picture quality over oldil~ly telephone wire can be obtained by using an NTSC video signal to frequency modulate a carrier signal and i..g only the carrier, close-în .si~1eb~n~ic~ and one outlying .si~leb~nr~
cont~ining the color subcarrier at 3.58 MHz, preferably the lower si~leban~l~ Inone ~;lilllt;llL, the carrier signal was centered at lO MHz approximately, close-in sideb~n~lc fell in the range of 9 to ll MHz, and the outlying lower si(leb~n-i fell at 6.42 MHz (i.e., lO MHz - 3.58 MHz). A SAW filter having a 3 dB
bandwidth of 6 MHz was used. Ihis p~CCb~ntl was frequency tr~nc1~t~d to fall b~Lwcell about S and ll MHz. The lower si-leb~n-l centered on 6.42 MHz actually has its own "sllbci-i~bands" which imitate in shape the close-in sidebands around lO MHz. It a~eals to be important to llal~.lliL these sub-sideb~n~lc withreasonable fidelity in order to m~int~in good picture quality. FYten~ling the filter p~ccb~n~l down to S MHz (i.e., about 1.6 MHz below 6.42 MHz) seems to satisfy this requirement.
Considering the simple phase modulation of a carrier with a low modulation index, the effect of suppressing one sideband is to convert the purely PCI'JUS9S/1494~i phase-modulated carrier into one which is cim-llt~nPol-~ly amplitude and phase ~ mo(~ t~l. If this signal is then passed through a limiter at the receiving end to ~u~-css the amplitude modulation, a pure phase modulation is restorcd, but with a halving of the modulation index. ~
By placing the carrier near the upper end of the pass band, so that the ~r~n~mittPA ~i~eb~n-l is the lower one, the effect of increasing ~ltenll~tion with frequency in the twisted-pair cable is to boost the lower si-leb~ntl relative to the carrier. This is in the oplu,lulll direction to co..~re~ e for the reduction in modulation index due to su~plcssion of the upper sicl~Pb~n-l. Rec~lse the sound carrier in each NTSC signal is located in the portion of spectrum which is "cut off" by tr~n~mittin~ only the lower ~ ob~n~i the audio signal may instead be mo~ ted onto an FM carrier and ~ d as FM1 or FM2, for example (see FIG. 2).
In duplex operation over UTP, filtering is required to separ~t~ the lr~ lp~l signal from the much weaker received signal, and some allowance - must be made for the guard or tr~n~ition bands of the filters used. Even in the case of a SAW filter, the transition band may be about 1 MHz wide. In various embotlim-ont~, a guard band width of 2 MHz has been l~ r~
Based on the above con~ P~ations, a frequency plan such as that illu~llaled in FIG. 2 is ~l~r~ d, but it is not intPn-lPA to limit in any way the principles of the invention. As one example, a proximal l~nsceiver may be located at the central telephone switch point, and a distal transceiver at a user's PCr/US9S114946 terminal such as in an office. The proximal tr~n~mitter carrier frequency may be 17 MHz, with nnminAl band limits of 13 to 19 MHz (signal B in FIG. 2).
The distal trAn~m~ r carrier may be 9 MHz, with band limits of 5 to 11 MHz (signal A in FIG. 2). Thus, the guard band is from 11 to 13 MHz. It is a sirnple matter to make minor adillctm~nt~ in these carrier freql~Pnries to O~IU1yelr~ llallce in any particular application.
As the losses illustrated in Table 1 show, the predicted loss of 2000 ft of UTP level 3 will be about 76 dB at 17 MHz, but only about 56 dB at 9 MHz, or 20 dB less. Since there is a need for some minimnm carrier-to-noise ratio at the receiver, it is desirable to transmit with more power at 17 MHz than at 9 MHz.
Still another consideration is that second harmonic distortion of the 9 MHz carrier, at 18 MHz, will have to be strongly ~up~lessed at the distal station in order to avoid illl~lr~.~,.lce with the weak received carrier at 17 MHz. Thusit is folLuiL.~us that the 9 MHz carrier can be relatively weaker. In the case of the 17 MHz IlA~ e~-7 hArmonir components at 34 MHz and above will be well removed from the receiver pA~bAn~l ,A~ ming a noise figure of 10 dB in the receiver, together with a noise bandwidth of 6 MHz, a received signal strength at the distal station of -59 dBm should yield a video signal-to-noise ratio of about 37 dB, which should be ~leql~t~ for most yulyoses.

FI~. 3 illustrates in block diagram form components used for carrying out the principles of the present invention btLw~en a first !.An~cei-ler 1 and a second llallSCei-/e~ 2. As illustrated in FIG. 3, llanscei~,r 1 accepts a first video signal V~NI and, after proceccing it in accordance with the principles of the invention, S tr~AncmitC it over wire UTP to llallscel~er 2, which lcgc~lates the original signal and outputs video signal VOUT2 for display on a television rece;~,el. Similarly, ll~nscei~,r 2 accepts a second video signal VIN2 as input and, after procPssing it in accordallce with the principles of the invention, tr~ncmirc it over the same UTP to l,a~lsc~i~,.,l 1, which ~ge~ at~s the original signal and outputs video signal VOUTI- The input video signals may be ge~-kl~r,~l from a carnera, a VCR, c<"l,~uleL, or the like, and the output signals may be provided to a display or ~~,coldi~g device such as a video m(~nitl~r, another VCR, or a co,..~ er video display.
Wire UTP may also be col~ to one or more tehPph~ nPs TEL and to a ~wi~hillg unit (such as a PBX or Centrex), such th-at normal telephone co,~ lions may be made over the same wire while the video signals are being ~lA~ ~3, It should also be a~par~ll that while bidirectional trAn~mi~sion with two L~dl~ceive~ is illustrated, it is of course possible for two video signals to be ~rAn~mittPfl from a first location to a second location, each signal using a separate carrier frequency. In that case, two trAn~mhting circuits would be required at one end and two ,~ceivi"g circuits at the other.

WO 96/17474 PCI~/US9S/14946 Begirming with transceiver 1, a first video signal VINI is input to VCO/amplifier/mixer VCO1 having a carrier frequency of, for exarnple, 17 MHz. The input video signal in~ les ll-min~n~e and chromin~nre components as is known in the art and as illustrated in FIG. 1(a), and frequency nnodulation S of this signal will produce upper and lower ~i~leb~n~c, each si~leban~l.having a "copy" of the color subc~ . Although FIG. 1(b) shows the ~ um of an AM-mo~ te~1 signal, the spectrum of an FM-mo~lnl~tPd signal will be similar even though the signal is ~lirÇclclll. As noted previously, the signal mo~lnl~t~l onto the 17 MHz carrier is preferably amplified relative to the signal mo~
onto the 9 MHz carrier in order to compen~ for ~tten~tion losses at the higher freqllen- ;.es.
The frequency mo~lnl~t~A signal is passed through band pass filter BPF1 with a 6 MHz pass band ~ 13 to 19 MHz, ~lthollgh since in the frequency plan of FIG. 2 no signals are ll,.,.~...i~PA above 19 MHz, this filter functions to match impe(l~n~es and to provide ~u~c~,sion of h~nnonics of 17 MHz. The filtered signal is input to balun L~iru~ er and hybrid circuit H1, which injectsthe signal into line UTP through diplex filter DFl. The l ull ose of the diplexing filter is to inject video modem signals onto the U~P while ~levelltillg video modem signals from entering the line.
Since the upper sicieb~nfl has been removed, the signal injected from H1 has a frequency spectrum roughly shown by B illustrated in FIG. 2. Other data signals such as Dl may be input as illustrated in the frequency plan of FIG. 2 with a~p~ iate modulation. Thus, for example, te~min~l DINI may be used to accept a data signal (such as an audio signal) which is m~ t~d by digital modulator DM1 and s~lbseq)ently passed through filter BP~6 and injected into hybrid Hl. Recovery of the signal in transceive~ 2 is through filter BPF10 and digital demodulator DD2 to output terminal DoUT2. Although not explicitly shown in Figure 3, an FM modulator may also be included to lla~ il frequency modulated audio signals such as FM1 and FM2 illustrated in FIG. 2, corresponding to video signals A and B respectively.
RecA~se the cc,~ ollell~ in llanscei~,e~ 2 on the right side of FIG. 2 are similar to those on the left side (but using different frequency bands), the l~ceiv,llg function will be described with refe,~llce to ~lallsceiver 1, and thecorresponding explanation for llal~scei~ 2 is omitted for the sake of brevity.
.g that tl~ce;~r 2 transmits a second video signal to transceiver 1 over wire UTP (illustrated by signal A of FIG. 2), the signal is received in H1 and applied to band pass filter BPF2 having a ~Ic;felled band pass range of S to11 MHz. The filtered signal is applied to preamp and upcoll~ C1. In FIG.

3, each l~,ce;~ iS of the ~u~.helerodyne type, using a local oscill~tQr and mixer to u~convell the signal to the 46 MHz center frequency of a SAW filter. This approach allows available SAW filters to be used, and has the further advantage - 20 of allowing the frequency plan to be modified. It should be noted that custom filter designs may be used in~te~(l, which el;.--i-.Al~,s the need for frequencyconversion.

PCrlUS9S/14946 SAW filter BPF3 provides an amplified output to limiter/discriminator/video amp L2, which further amplifies the output to video levels (NTSC, PAL or SECAM) and the recovered video signal is output as VOUTI- It has been determin~l that excellent results are obtained with no pre-S e~lnrh~ or de-emphasis of the signal.
~IG. 4 shows a tiet~ d s~ employing the principles of the present Lnvention. The circuit operates from regulated +5 and + 12 VDC supplies. The lld~ ni~ VCO U6 is a multivibrator wit'n a relatively linear control characteristic. In the present invention, FM deviation is typically large compared to the carrier frequency so that moderate drift of center frequency and phase noise are of little concern.
The NTSC video input in~ ing the color subcarrier is applied at E5, and is passed through a low pass filter having a cutoff of about S MHz.
The mul~ ib,aLol output is AC~oupled to one section of U4, a hex buffer which amplifies the mulliviblatol levels to 0 to 5 VDC. The amplified output drives the rem~ining 5 section~ of U4 in parallel.
Since the hex buffer output is a square wave with numerous harmonics, it is i~ Jol~ll to design the following filter so that it has a high input impedance at the frequencies of these harmonics; i.e., the f,rst circuit elt~m~nt must be a series inductor.
In the 17 MHz case, the output filter functions chiefly to match 7.5 o'nms to a 50 ohm output impedance, and to provide moderate ~u~Jp~S~.iOn of CA 0220652l l997-05-30 PCI'/US9S/1'1946 harrnonics of 17 MHz. In the 9 MHz case, the filter must also provide attem~tion of the second harmonic at 18 MHz.
In the case of the receive fllters, the filters are typically ~leci~Pll for a 50ohm input impedance, and a higher output impedance such as 400 or ~00 ohms.
S The ill~ ase in impedance provides a voltage gain working into the relatively high input im~pedance of the U5 frequency converter.
Filters initially desi~nrd to pass the 9 MHz carrier were implemP-nt~d using fe~ colc inductors from a coil kit. High and mysteriously variable levels of second harmonic energy at 18 MHz were observed. These were found to be caused by non-linear distortion in the ferrite cores, which depended also on theol;c~ ioll of the cores relative to the earth's m~gnetic field; i.e., a fl~-xg~tr m~netc-mrter had been inadv. .Lt;llLly implemerlte~l Therefore, the use of aircore solenoids is recomm~nrled The output of the Lldllslllil b~ C~ filter is applied to a transforrner T1 which sim-llt~n~ously acts as a balun and as a 3 dB hybrid. In this transformer,4 and 7 are the b~l~nroA output driving the UTP with a nomin~l gelleldtor ;~ re of 100 ohrns.
Termin~l~ S and 6 of lla~rol,ller T1 are ~hllnt~ by C~r~CitQr C1, which is a relative short circuit above about 1 MHz. Signals or DC voltages below 1 MHz may be made available at 1~ AUX1 and AUX2 for use with other e~ nt Termin~l~ 1 and 3 are ml~ lly isolated 50 ohm ports of the hybrid.
A 25 ohm load at terrninal 2 in effect t~rmin~tes the "sum" port of the hybrid PCrlUSgS/14946 transformer. The data signals can be coupled in using a diplexing filter desi~n.od to have a bro~-lb~n~1 input and two outputs, one co.l~i,yollding to signals fromDC to about 4 MHzt and the seco~l, to signals from S MHz to above 20 MHz.
In the receive path, the received signal out of termin~l 1 of transformer Tl is applied to receive filter BPF5 (BPF2) in the distal (proximal) transceiver.
As noted previously, BPF2 should be ~t~ci~nPd to provide rejection in ~he band 13 to 20 MHz, en~olllp~c~ g the 18 MHz harrnonic.
The filtered signal is applied to U5, a frequency converter device which combines the functions of a local oscill~tor and an active mixer. Back-to-back diodes U3 shunt the input to U5 in order to handle the strong received signals which would occur when the UTP line is short.
The U5 output has a generator impedance of about 1.5K. PNP emitter follower Q1 helps to bring this impe(l~n~e down towards the 50 ohm input impedance of the Q2 stage. The Q1 emitter follower also helps to stabilize the DC opeldlillg point of the Q1-Q2 cascade against variation in VBE with t~m~ature. The Q2 stage provides about 30 dB of voltage gain together with a high output capability (relative to the +5VDC supply voltage) due to the use of L3 as a collector load. The Q2 stage has a low output impe l~nre as is desired to improve SAW filter response.
The U7 SAW filter operates into a b~l~n~ load for improved input-output isolation. The small shunt capacitor, C29, slightly improves the shape ofthe SAW filter pass band.

The amplified output of the SAW filter is applied to U10, a limiter-discriminator circuit. Apart from an adjl~ctm~nt of the quadrature coil network for wideband operation at 46 MHz, this circuit yields good limitin~ action over a 40 dB range, with excellent discriminator linearity.
Wideband buffer U9 and op amp U8 implement a dirrc~ ial input video amplifier to amplify the output of the disc,;~ u~or to NTSC video levels. The ripple frequency at the output of U10 is about 92 MHz. Thus s~mple lowpass filtering by C2~ and C33 provides adequate rejection of ripple in the video output.
With respect to pre-l-mph~si~ of the signal applied to the FM modulator, it is perceived as a distinct advantage of the present invention that no pre-emphasis and de-emphasis is nP~ed, although the invention will of course operate with such additional Cil-;uill,~.
FIG. S shows how the prinrirles of the present invention can be employed to tl~u~lllil data displayed on a coll,yu~ monitor. Computer S01 may be a PC-type cc"..~u~er having a red-green-blue (RGB) output which is supplied to a scancoll~el~l 503 which is well known in the art. The RGB signal from co-l~l~uler 501 is input to col~pul~l monitor 502 to drive its display. Scan converter 503 converts the RGB signals ~o a video format such as NTSC format, and supplies it to video modem 504 which is constructed in accordance with the principles of the present invention and coupled to telephone line UTP. Thus, data which is wo 96/17474 Pcr/uss5ll4946 displayed on computer monitor 502 may be tr~n~mitted over telephone line UTP
and simlllt~npously displayed on another monitor at the receiving end.
Thus has been described a method and apparatus for tr~n~mittin~
television-quality video signals as well as other signals over ordinary telephone-grade wire in accGldallce with a suggested modulation scheme and frequency plan. The invention has many possible uses and benefits, and ~.Çol-~ s the desired functions with a mi~ --- of circuit components.
The above description and accompanying drawings provide various preferred embo~lim~nt~ of the present invention. It will be understood by one ofordinary skill in the art that specific l~r~r~l~ces to components herein are by way of exarnple only, the specific devices and device values being tlict~t~l by the particular l~quirelllents and e~in~ering tradeoffs involved in a particular implt?m~nt~tion. As one e~ le, it will be appreciated that the various filters and dem~~ tor.~ can be impl~ A with a digital signal proces~ing device instead of using analog col--pollell~. It will be a~al~ that many mo~lifi~tions and variations of the present invention are possible in light of the above te~chin~. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims (34)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for transmitting moving video information over a single pair of unshielded twisted pair (UTP) wires, comprising the steps of:
(1) frequency modulating a first carrier signal in accordance with a first composite video signal having a luminance component and a color subcarrier and producing thereby a first FM
signal comprising a first upper sideband and a first lower sideband each including said color subcarrier of said first composite video signal;
(2) filtering said first FM signal with a first band pass filter to suppress one of said first sidebands and to pass the other of said first sidebands, and producing thereby a first filtered signal having a frequency bandwidth less than that of said first FM signal;
and (3) from a first physical location, injecting said first filtered signal into said single pair of UTP wires.

2. The method of claim 1, further comprising the steps of:
(4) from a second physical location, receiving said injected first filtered signal from said single pair of UTP wires;
(5) filtering said received first signal to isolate it from other signals on said single pair of UTP wires; and (6) frequency demodulating said isolated signal obtained at step (5) and outputting it to a first display device.

3. The method of claim 2, further comprising the steps of:
(7) at said second physical location, frequency modulating a second carrier signal in accordance with a second composite video signal having a luminance component and a color subcarrier and producing thereby a second FM signal comprising a second upper sideband and a second lower sideband each including said color subcarrier of said second composite video signal;

(8) filtering said second FM signal with a second band pass filter to suppress one of said second sidebands and to pass the other of said second sidebands, and producing thereby a second filtered signal having a frequency bandwidth less than that of said second FM signal;
and (9) injecting said second filtered signal into said single pair of UTP wires.

4. The method of claim 3, further comprising the steps of:
(10) from said first physical location, receiving said injected second filtered signal from said single pair of UTP wires;
(11) filtering said received second signal to isolate it from other signals on said single pair of UTP wires; and (12) frequency demodulating said isolated signal obtained at step (11) and outputting it to a second display device.

5. The method of claim 1, wherein step (1) comprises the step of using an NTSC
video signal to frequency modulate said first carrier signal and producing said first FM signal with said color subcarrier located approximately 3.58 MHZ above a center frequency of said first carrier signal.

6. The method of claim 1, wherein step (1) comprises the step of using a PAL
format video signal to frequency modulate said first carrier signal.

7. The method of claim 1, wherein step (1) comprises the step of using a SECAM
format video signal to frequency modulate said first carrier signal.

8. The method of claim 1, further comprising the step of injecting a modulated data signal into said single pair of UTP wires concurrently with and separated in frequency spectrum from said first filtered signal.

9. The method of claim 8, wherein said step of injecting said modulated data signal comprises the step of injecting a digitally modulated data signal into said single pair of UTP

10. The method of claim 8, wherein said step of injecting said modulated data signal comprises the step of injecting a separate FM-modulated audio signal into said single pair of UTP wires.

11. The method of claim 1, wherein step (1) is conducted without performing any pre-emphasis of said first composite video signal.

12. The method of claim 1, wherein step (3) comprises the step of using a pair of UTP
wires having a length of between approximately 20 and 2,000 feet and which are incorporated into an office building, said pair of UTP wires being used primarily for telephone communications.

13. The method of claim 2, further comprising the step of injecting a telephone voice signal into said single pair of UTP wires.

14. Apparatus for transmitting moving video information over a single pair of unshielded twisted pair (UTP) wires, comprising:
first frequency modulation means for frequency modulating a first carrier signal in accordance with a first composite video signal having a luminance component and a color subcarrier and for producing thereby a first FM signal comprising a first upper sideband and a first lower sideband each including said color subcarrier of said first composite video signal;
first filtering means, coupled to said first frequency modulation means, for filtering said first FM signal to suppress one of said first sidebands and to pass the other of said first sidebands, and for producing thereby a first filtered signal having a frequency bandwidth less than that of said first FM signal; and first injecting means, coupled to said first filtering means, for injecting said first filtered signal into said single pair of UTP wires at a first physical location.

15. The apparatus of claim 14, further comprising:
first receiving means for receiving, at a second physical location, said injected first filtered signal from said single pair of UTP wires;
second filtering means, coupled to said first receiving means, for filtering said received first signal to isolate it from other signals on said single pair of UTP
wires; and first demodulating means, coupled to said second filtering means, for frequency demodulating said first isolated signal and outputting it to a first display device.

16. The apparatus of claim 15, further comprising:
second frequency modulation means for frequency modulating a second carrier signal in accordance with a second composite video signal having a luminance component and a color subcarrier and for producing thereby a second FM signal comprising a second upper sideband and a second lower sideband each including said color subcarrier of said second composite video signal;
third filtering means, coupled to said second frequency modulation means, for filtering said second FM signal to suppress one of said second sidebands and to pass the other of said second sidebands, and for producing thereby a second filtered signal having a frequency bandwidth less than that of said second FM signal; and second injecting means, coupled to said third filtering means, for injecting said second filtered signal into said single pair of UTP wires at said second physical location.

17. The apparatus of claim 16, further comprising:
second receiving means for receiving, at said first physical location, said injected second filtered signal from said single pair of UTP wires;
fourth filtering means for filtering said received second signal to isolate it from other signals on said single pair of UTP wires; and second frequency demodulating means for demodulating said second isolated signal and outputting it to a second display device.

18. The apparatus of claim 14, further comprising means for injecting a modulated data signal into said single pair of UTP wires concurrently with and separated in frequency spectrum from said first filtered signal.

19. The apparatus of claim 18, further comprising a digital modulator for digitally modulating a data signal and producing said modulated data signal.

20. The apparatus of claim 18, further comprising an FM modulator for frequency modulating an audio signal and producing said modulated data signal.

21. The apparatus of claim 14, further comprising means for coupling and transmitting a telephone voice signal on said single pair of UTP wires concurrently with said first filtered signal.

22. A video device comprising:
an input terminal for accepting a first composite video signal having a first luminance component and a first color subcarrier;
a telephone terminal connectable to an unshielded twisted pair telephone line;
an FM modulator, coupled to the input terminal, which modulates the first composite video signal onto a carrier signal and produces thereby a first FM signal comprising a first upper sideband and a first lower sideband each including information from the first color subcarrier;
a bandpass filter coupled to the FM modulator and having a passband which suppresses one of the first sidebands and passes the other of the first sidebands, and which produces therefrom a first filtered FM signal having a bandwidth less than the first FM
signal; and a transformer coupled between the bandpass filter and the telephone terminal which drives the telephone terminal in accordance with the first filtered FM signal.

23. The video device of claim 22, further comprising:
an output terminal for producing a second composite video signal having a second luminance component and a second color subcarrier;
a receive filter, coupled to the transformer, for isolating signals received from the telephone terminal in a different frequency band from the first filtered FM
signal; and an FM demodulator, coupled between the receive filter and the output terminal, which demodulates signals from the receive filter and outputs them to the output terminal.

24. The video device of claim 23, wherein the first and second composite signals comprise NTSC video signals each having separate color subcarriers.

25. The video device of claim 23, further comprising a digital modulator which digitally modulates audio information and a filter circuit which filters the digitally modulated audio information and injects it onto the unshielded twisted pair telephone line.

26. The video device of claim 23, further comprising a diplex filter which couples a telephone voice signal to the telephone terminal.

27. A method for transmitting moving video information over a single pair of unshielded telephone wires, comprising the steps of:
(1) using a frequency modulation modulator to frequency modulate a carrier signal using a composite moving video signal comprising a luminance component and a chrominance component as a modulating signal, and producing thereby a frequency modulated carrier signal comprising an upper sideband and a lower sideband each comprising modulated portions of the composite video signal;

(2) filtering the frequency modulated carrier signal to suppress one of the sidebands and producing thereby a filtered signal having a frequency bandwidth less than that of the frequency modulated carrier signal; and (3) injecting the filtered signal into the single pair of unshielded telephone wires.

28. The method of claim 27, further comprising the step of simultaneously transmitting a voice telephony signal on the single pair of unshielded telephone wires, wherein the filtered signal is located in a frequency space which does not interfere with the voice telephony signal.

29. A video modem comprising:
an input terminal which accepts a first moving video signal;
a first telephone terminal connectable to an unshielded twisted pair telephone line;
an FM modulator, coupled to the input terminal, which frequency modulates the first video signal onto a carrier signal and produces thereby a first FM signal comprising a first upper sideband and a first lower sideband;
a transformer circuit, coupled to the first telephone terminal, which drives the first telephone terminal in accordance with the first FM signal;
an output terminal which provides a second moving video signal;
a receive filter, coupled to the transformer circuit, which isolates a second moving video signal received from the first telephone terminal in a frequency band different from the first FM signal; and an FM demodulator, coupled to the receive filter and the output terminal, which demodulates signals from the receive filter and provides them to the output terminal.

30. The video modem of claim 29, wherein the first and second moving video signals each comprise composite color video signals.

31. The video modem of claim 29, further comprising a bandpass filter coupled between the FM modulator and the transformer circuit and having a passband which suppresses one of the first sidebands and passes the other of the first sidebands, and which produces therefrom a first filtered FM signal having a bandwidth less than the first FM
signal.

32. The video modem of claim 29, further comprising:
a second telephone terminal which accepts a voice grade telephone signal from a telephone; and a diplex filter, coupled between the second telephone terminal and the first telephone terminal, which couples the voice grade telephone signal to the first telephone terminal to permit voice grade communication over the telephone line without interfering with the first and second moving video signals.

33. The video modem of claim 29, further comprising:
a data input terminal which receives a data signal;
a data signal modulator, coupled to the data input terminal, which modulates the data signal; and a data transmit filter, coupled between the data modulator and the transformer circuit, which filters the modulated data signal and provides the filtered data signal to the transformer circuit and thereafter to the first telephone terminal.

34. The video modem of claim 33, further comprising:
a data output terminal which provides a second data signal;
a data receive filter, coupled to the transformer circuit, which isolates a modulated version of the second data signal present at the first telephone terminal; and a data demodulator, coupled between the data receive filter and the data output terminal, which demodulates the isolated modulated version of the second data signal and provides the demodulated signal to the data output terminal.